1. Field of the Invention
The present invention relates to a wireless IC tag reader, and more specifically relates to a wireless IC tag reader having a function for reading information stored in a wireless IC tag (the wireless IC tag is also called an electronic tag or a radio frequency identification (RFID) tag).
2. Description of the Related Art
An RFID technique is recently used. In the RFID technique, a tag communication device (wireless IC tag reader) which is a reader or a reader/writer carries out wireless-communication with a wireless IC tag to read information stored in the wireless IC tag remotely. Especially, the wireless IC tag is expected as an alternative to a bar-code in a physical distribution field. In the near feature, it is predicted that the RFID technique spreads widely.
For example, the RFID technique is applied to detection to be carried out when a product enters into or leaves from a warehouse or a store. In this case, it is important to surely read multiple pieces of information stored in wireless IC tags incorporated in products within a communication area. Generally, in the communication area, there are weaker radio wave spot areas (these areas are also called field holes, dead spots or null points) where radio waves from a wireless IC tag reader interfere with each other on multiple paths by reflection phenomena and the radio waves are almost canceled. If a wireless IC tag is located in a dead spot, it is difficult or impossible for the wireless IC tag reader to read information stored in the wireless IC tag.
As a method for resolving the above-described problem, Japanese Patent Application Laid-Open No. 2006-20083 discloses a control method for electronically controlling directional characteristics (angular characteristics) of radio waves to be transmitted by a wireless IC tag reader (see paragraphs [0054] to [0059] and FIG. 2).
In the control method, a common type in which antennas for transmitting radio waves and receiving response waves are commoditized is employed. However, it is difficult to separate a response wave transmitted by a wireless IC tag from a radio wave transmitted by a wireless IC tag reader because the intensity of response wave is remarkably lower than that of radio waves transmitted by the wireless IC tag reader. In order to resolve the above-described problem, a separate type in which antennas for transmitting radio waves and receiving response waves are separated is recently employed.
The separate type however increases a cost because the antennas for transmitting radio waves and receiving response waves are separated. Further, if a radio wave transmitted from the separate type antenna has relatively high intensity so as to be uniformly transmitted to a wide area while being kept at a certain level, the dead spots still appear in a communication area.